Method and device for degassing liquids

ABSTRACT

1. METHOD OF DEGASSING A LIQUID FLOWING IN A FILM ALONG THE INNER PERIPHERAL SURFACE OF A ROTATING CENTRIFUGE ROTOR, WHICH COMPRISES DIVIDING THE LIQUID, BEFORE IT LEAVES THE ROTOR, INTO A FRACTION HAVING A LOW GAS-BUBBLE CONTENT AND A FRACTION HAVING A HIGH GAS-BUBBLE CONTENT, SEPARATELY REMOVING THE FRACTION HAVING A HIGH GAS-BUBBLE CONTENT, AND SEPARATELY REMOVING THE LIQUID FRACTION HAVING THE LOW GAS-BUBBLE CONTENT FROM THE ROTOR IN A MANNER TO MINIMIZE THE ADDITION OF FURTHER GAS-BUBBLE THERETO.

United States Patent [11] 3,856,483 Rumpi et al. Dec. 24, 1974 METHOD AND DEVICE FOR DEGASSING [56] References Cited QUIDS UNITED STATES PATENTS [75] Inventors: Hans Rumpf, Hansjakobstr. 12, 75 2,634,907 4/1953 Smith 55/52 X Karlsruhe; Kurt P. Lcschonski, 3,271,929 9/!966 Bowden et al 55/203 X la us Thal zellerfeld; Helmar Schubert, Karlsruhe-Durlach, all P I E S h N Z h f G rimary xammer ami a arna O ermany Assistant ExaminerR. W. Burks [73] Asslgnee? Hans Rumpf, Karlsruhe Germany; Attorney, Agent, or FirmHerbert L. Lerner et al.

by said Leschonski and said Schubert [57 ABSTRACT [22] Filed: Sept. 21, 1972 21 Appl. 291 031 Method of degassing a liquid flowing in a film along the inner peripheral surface of a rotating centrifuge rotor includes dividing the liquid, before it leaves the [30] Forelgn Apphcauon Pnomy Data rotor, into a fraction having a low gas-bubble content p 2i, i971 Germany 2147124 and a fraction having a high gas-bubble content, and removing the liquid fraction having; the low gas-bubble [52] U.S. Cl 55/38, 55/52, 55/203 content from the rotor in a manner to minimize the [5 l] Int. Cl Bfild 19/00 addition of further gas-bubbles thereto; and device for [58] Field Of Search 55/38, 41, 52, 178, 199, carrying out the method,

11 Claims, 4 Drawing Figures PATENTEB BEBE 4 I974 FEGA The invention relates to a method and device for degassing especially viscous or highly viscous liquids in a film flowing along the inner peripheral surface of a centrifuge rotor, and preferably with the use of vacuum.

Many products of the chemical, pharmaceutical, food and related industries, such as highly viscous liquids including pastes, suspensions, emulsions, for example, contain air or gases dissolved therein or present in the form of small bubbles which are unavoidably formed in the liquid during the production thereof but which should not or must not be contained in the final product. Thus, for example, gas bubbles present in salves or ointments of the pharmaceutical industry detract from the appearance of the ointment in its container and prevent accurate and continually unvarying filling of the containers therefor. Pastes or emulsions of the food industry must often contain no air in order to avoid premature aging or deterioration, and the same holds true for many normally viscous liquids.

Methods of degassing liquids in a centrifuge are known from German Non-prosecuted Published Application DOS 1 619 909, wherein the liquid, in the form of a thin layer, is subjected to a radial acceleration acting substantially perpendicularly to the thin layer at an ambient pressure greater than the vapor pressure of the liquid phase. in the centrifugal field, an inwardly directed impetus or buoyancy acts upon the gas bubbles present in the liquid and transports them inwardly.

It has been found to be particularly expedient to degas a liquid in a film flowing along the inner peripheral surface of a centrifuge rotor. A primary advantage thereof is that only a relatively low overpressure develops in the liquid with respect to the outer pressure of the gas chamber prevailing at the surface of the film. Consequently, only a minimal amount of gas is additionally dissolved in the liquid and has to be liberated again when the degassed liquid is subsequently discharged. With degassing centrifuges having relatively high liquid levels, such as are known in the patent literature and employed in technical practice, this fact is evidently disregarded, with the disadvantageous consequence, especially, that the fine particles are deprived of the degassing operation due to dissolving and subsequently occurring bubble reformation.

For these reasons, the method ofthe invention of the instant application is based on the heretofore known centrifugal separation of gas-bubbles in a liquid film. It has been found, however, that the bubble separation in a liquid film does not have quite the effect anticipated and corresponding to the theory of separation. It was determined, on the contrary, that the liquid which is again collected in the stationary part of the centrifuge may have the identical or sometimes even a higher gasbubble content than that ofthe liquid being supplied to the rotary part of the centrifuge. Consequently, degassing centrifuges with flowing liquid films have not been successful heretofore in actual practice. The negative effect therein results from two phenomena. First, even if vacuum is employed, relatively fine gas bubbles cannot leave the surface of the liquid within the time that is availabe, because equilibrium is established between the buoyancy of the bubbles protruding from the liquid and the surface tension of the liquid when the bubbles are less than a given size. Second, the liquid film flung out by the centrifuge rotor gathers a few gas bubbles again when it strikes the casing wall of the centrifuge.

It is accordingly an object of the invention to provide a method and device for degassing a liquid flowing in a film along the inner peripheral surface of a rotating centrifuge rotor which results in a degassing of the liquid which is superior to that of the liquid which is superior to that of the heretofore known methods and devices of this general type.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method of degassing a liquid flowing in a film along the inner peripheral surface of a rotating centrifuge rotor, which comprises dividing the liquid, before it leaves the rotor, into a fraction having a low gas-bubble content and a fraction having a high gasbubble content, and removing the liquid fraction having the low gas bubble content from the rotor in a manner to minimize the addition of further gas-bubbles thereto.

in two alternate modes of the method of the invention, the liquid fraction having the low gas-bubble content is removed from the rotor either while simulta' neously avoiding contact of that liquid fraction with gas which forms the bubbles, or after the peripheral speed of that liquid fraction is reduced.

The method of the invention indeed foregoes the obvious advantage of heretofore known methods of the general type in that no special measures whatsoever must be met for removing the gas bubbles because they vent through the surface of the liquid into the gas chamber. Due to the great simplicity of such a gas venting or discharge, all of the heretofore known degassing centrifuges therefore operate in this manner, apparently accepting in ignorance of the true relationships, that only relatively large bubbles are removable from the liquid even when vacuum is applied.

In accordance with the method of the invention, the separation of relatively fine gas bubbles is, in fact. sought to be effected. Specifically in accordance with a further feature of the method of the invention, a part or fraction of the liquid having gas bubbles accumulated in the surface layer thereof is drained off or dis charged. Insofar as no special use exists for this liquid concentrated with bubbles, in accordance with an additional feature of the invention, a major part of the bubbles is separated and the remainder is returned to the degassing film flow. This partial separation, is contrast to the draining or discharge of the fraction of the liquid having a low gas-bubble content, is effected with ample success by the impact thereof against a stationary wall in a vacuum. in spite of the additional expense and the greater liquid loading of the film, this method has proven to be advantageous because of the relatively high standard of degassing achieved thereby.

The degassing of the liquid is employable with particular success with the use of the aforedescribed method of separation or division or, if it is only a matter of separating relatively large gas bubbles, the foregoing separation method may be dispensed with because, in order to avoid the aforementioned second basic disadvantage of the heretofore known methods, the fraction of the liquid having the low bubble content is withdrawn from the rotor either without coming into contact with gas that forms the bubbles or after previously reducing the peripheral speed thereof. Thereby, contrary to professional opinion heretofore, the use of centrifugal degassing ofliquid film for relatively fine gas bubbles has become possible industrially because the take-up, once again, or reabsorption of gas bubbles during the collection of the degassed liquid is largely prevented.

It has been found that the reabsorption or reinclusion of gas bubbles depends very decisively upon the relative velocity between the ejected liquid and the stationary wall of the centrifuge casing. The higher the relative velocity is, the more gas is intermixed with the liquid film accompanied by turbulent blending or mixing by partial disintegration or bursting of the liquid film. These disadvantages have been avoided, in accordance with the device of the invention by providing, for example, backwardly curving outlet channels on the centrifuge rotor for reducing the peripheral speed of the fraction of the liquid having the low bubble content. Due to this backward curving, the peripheral speed, which delivers the major component of the relative speed between the outwardly flowing film and the stationary centrifuge casing, is greatly reduced. In order that the velocity components directly backwardly relative to the rotor be as large as possible it is advantageous, in accordance with the invention, to construct the discharge or outlet channels ofthe rotor with downwardly tapering cross sections.

Another possibility for avoiding the admixture of air with the ejected liquid fraction having the low bubble content is that, in accordance with a further feature of the invention, contact with air is avoided altogether. The particular features of the invention for avoiding contact between air and the liquid fraction having the low bubble content is to provide a liquid chamber adjacent the rotor of the degassing centrifuge, the chamber being completely filled with liquid and being adapted to receive therein the liquid fraction having a low bubble content without contact of that liquid fraction with gas forming the bubbles. The liquid chamber and the rotor are mutually sealed by sealing means disposed adjacent the rotor or, for example, by a labyrinth or a groove seal which is soaked or rinsed through from the inside to the outside thereof by liquid.

In accordance with a concomitant feature of the invention, the open end of the centrifuge rotor has a rim which is surrounded by an annular collecting chamber that is adapted to receive therein from the rotor the liquid fraction having the low gas-bubble content, and means for draining the latter from the chamber while simultaneously avoiding contact thereof with gas forming the bubbles.

Although the invention is illustrated and described herein as method and device for degassing liquids, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The invention, however, together with additional objects and advantages thereof will be best understood from the following description when read in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic vertical sectional view of a degassing centrifuge for degassing liquids in accordance with the invention, including an annular member having a cutting edge for dividing the liquid fraction of low-bubble content from the liquid fraction of high bubble content, outlet channels for the liquid fraction having the low bubble content, and stationary collecting chambers for receiving both liquid fractions therein, respectively;

FIG. 2a is an enlarged fragmentary view of FIG. 1 showing a detail of the degassing centrifuge which ineludes the backwardly curving channels provided on the rotor to reduce the peripheral speed of the liquid fraction having the low bubble content;

FIG. 2b is a sectional view of FIG. 2a taken along the line IIb Ilb in the direction of the arrows;

FIG. 3 is a view similar to that of FIG. 1 of another embodiment of the degassing centrifuge according to the invention; wherein a liquid chamber is located adjoining the rotor and into which the liquid fraction having the low bubble content is receivable without being in contact with gas which forms the bubbles; and

FIG. 4 is a view corresponding to those of FIGS. 1 and 3 of yet another embodiment of the degassing centrifuge wherein discharge of the liquid fractions having the low and high gas-bubble contents, respectively, is effected by a draining device that is stationary or is rotatable slowly with and relative to the centrifuge rotor.

Referring now to the drawing and first, particularly to FIGS. 1, 2a and 21) thereof, there is shown therein a degassing centrifuge constructed in accordance with the device of the invention for carrying out the method of the invention. As shown in FIG. 1, liquid to be degassed is introduced through an inlet in the bottom of the centrifuge into a centrifuge rotor 2 which is bowlshaped and slightly widens upwardly in conical form to an open top thereof. As the rotor 2 rotates, the liquid accelerates in peripheral direction of the rotor 2 and spreads over the inner wall surface of the rotor 2 in a rising thin film 3. Degassing of the liquid occurs as the film 3 is carried upwardly long the inner wall surface of the rotor 2, which is, for example, approximately 10 cm to l m long (high) until, at the upper end of the rotor 2, a liquid layer having a low-bubble content has formed adjacent the wall of the rotor 2, and a liquid layer having a high-bubble content has formed thereon. Both of these component layers are divisible from one another by a retractable annular, substantially cylindrical member 4 having a cutting edge and being in the form of an overflow or weir. By means of the cutting edge member 4, the liquid component or fraction 5 having the high gas-bubble content is directed into a collecting channel or duct 6 and therefrom, after partial separation of the bubbles, is recycled through an outer tube or duct 7 and through the bottom inlet to the rotor 2 into the supplied flow of the film being degassed in the rotor 2. The partial separation of the bubbles is effected, for example, by flinging or casting the liquid fraction having the high gas-bubble content from a horizontal part of an overflow or weir 8, which is connected at the top thereof to the cutting edge member 4, and by causing it to impact with an opposing cylindrical wall of the draining or collecting duct or channel 6 under vacuum.

The liquid having the low gas-bubble content leaves the rotor 2 through backwardly curved draining ducts or channels 10 (note FIGS. 2a and 2b, particularly), and is transferred at low peripheral and radial velocity to a stationary, slightly conical annular lid or cover 11 of a draining duct or channel 12. The transfer of the liquid fraction having the low bubbles content should be effected as smoothly as possible, and therefore the liquid leaving the draining channels 10 should, if possible,

impinge on the lid 11 tangentially. A detail of the eentrifuge for the transfer of the liquid fraction 13 having the low bubble content and the liquid fraction 5 having the high bubble content is shown in enlarged view in FIG. 2a. In the cross-sectional view of FIG. 2b, there can be seen the exemplary shape of the backwardly curved draining channels by means of which the peripheral speed of the liquid fraction having the low gas or bubble content is reduced.

FIG. 2a shows in section part ofthe degassing centrifuge of the invention whose operation has already been described hereinbefore with respect to FIG. I. The overflow 4', 8 formed with a cutting edge is shown both in FIGS. 1 and 2a as a member rotating with the centrifuge rotor. This affords advantages with respect to production techniques, since the thickness of the film is only in the order of magnitude of millimeters and the spacing between the cutting edge 4 and the inner wall surface of the rotor must be accommodated or adjusted to the thickness of the film. In principle, however, it is also possible to employ a stationary non-rotating overflow 4, 8 instead of a rotary one.

In FIG. 3, there is shown another embodiment ofthe centrifuge of the invention wherein the rotor adjoins a liquid chamber into which the liquid fraction having the low gas-bubble content has passed without coming into contact with any of the gas that forms the bubbles. A suitable outlet aperture 14 which, in its simplest form, is an annular peripheral slot or a row of sieve holes, is provided in the rotor wall. The peripheral speed is reduced by friction in the initially static liquid ring 15. In the liquid ring 15, during stationary opera tion, an outwardly decreasing peripheral speed is established. In order to afford the transfer of the liquid having the low gas-bubble content without permitting contact thereof with gas that might form additional bubbles therein, the gas must be prevented from penetrating from the outer chamber 16 (FIG. 3). For this reason, sealing with respect to the outer chamber 16 must be effected. The seal 17 accordinly provided for that purpose is, for example, a packing adjacent the rotor or a labyrinth or groove seal, it being advantageous for the seal to be soaked through outwardly from the inside thereof with liquid in order to prevent any gas from penetrating therethrough. With the embodiment of FIG. 3, there is also provided a cutting edge member or film splitter 4 that rotates with the centrifuge rotor.

In FIG. 4 there is shown yet another embodiment of the degassing centrifuge wherein the removal of the liquid fraction having the low gas content and the liquid fraction having the high gas content is effected by a stationary draining device or one that rotates slowly with the centrifuge rotor. In the embodiment of FIG. 4, a rotationally symmetrical draining device for the liquid fraction having the low gas content and for the liquid fraction having the high gas content is provided. In this embodiment of the centrifuge, the two fractions of the liquid are again divided from one another by a cutting edge member or film splitter 4. The liquid fraction having the low bubble content is, however, accumulated or collected in an annular collecting chamber 20 and removed therefrom by the draining device. The draining device is formed, for example, of slightly conical metal plates 21 which are disposed above one another and which define therebetween rotationally symmetrical chambers for carrying away the liquid fractions. At the outer periphery of the rotor, there are located radially or curved scoops 18 and 19, which skim off the liquid fractions. Instead of the rotationally symmetrical construction shown in FIG. 4, individual draining channels or tubes can be provided which taper to a point at the forward end thereof and skim or scale off the liquid fractions.

In the illustrated embodiments, the centrifuge is disposed so as to be vertically oriented and open at the top thereof. Similarly, devices within the scope of the invention can be conceived of wherein, for example. the centrifuge is operable with an open bottom end. This type of orientation may be advantageous for discharging parts of the liquid from the centrifuge.

We claim:

1. Method of degassing a liquid flowing in a film along the inner peripheral surface of a rotating centrifuge rotor, which comprises dividing the liquid, before it leaves the rotor, into a fraction having a low gasbubble content and a fraction having a high gas-bubble content, separately removing the fraction having a high gas-bubble content, and separately removing the liquid fraction having the low gas-bubble content from the rotor in a manner to minimize the addition of further gas-bubbles thereto.

2. Method according to claim 1 wherein the liquid fraction having the low gas-bubble content is removed from the rotor while simultaneously avoiding contact thereof with gas forming the bubbles.

3. Method according to claim 1 wherein the liquid fraction having the low gas-bubble content is removed from the rotor after reducing the peripheral speed thereof.

4. Method according to claim 1 which includes returning the liquid fraction having the high gasbubble content to the flowing liquid film after liberating part of the gas bubbles from the last-mentioned liquid frac tron.

5. Degassing centrifuge for carrying out a method of degassing a liquid flowing in a film having respective liquid layers with a low and high gas-bubble content, comprising a rotor having an open end, and overflow and dividing means located at said open end for dividing a liquid film flowing along the inner peripheral surface of said rotor into a liquid fraction having a low gas bubble content and a liquid fraction having a high gasbubble content before separately removing said liquid fractions from said rotor, said overflow and dividing means being adjustable to the thickness of the liquid layer having the low gas-bubble content.

6. Centrifuge according to claim 5 wherein said overflow means is formed with a cutting edge.

7. Centrifuge according to claim 5 including backwardly curving outlet channels located adjacent said open end of said rotor and adapted to receive therein, during rotation of said rotor, the liquid fraction having the low gas-bubble content and to reduce the peripheral speed thereof.

8. Centrifuge according to claim 5 including an annular liquid chamber adjacent said rotor and surrounding said open end thereof, and means for transferring the liquid fraction having the low gas-bubble content from said rotor to said liquid chamber while simultaneously avoiding contact thereof with gas forming the bubbles.

9. Centrifuge according to claim 5 wherein said open end of said rotor has a rim, and including an annular collecting chamber surrounding said rim and adapted to receive therein from said rotor the liquid fraction having the low gas-bubble content, and means for draining the last-mentioned liquid fraction from said draining means is stationary with respect to said rotor.

11. Centrifuge according to claim 9 wherein said chamber while Simultaneously avoiding Contact thereof draining means 18 slowly rotatable with respect to said with gas forming the bubbles.

l0. Centrifuge according to claim 9 wherein said 

1. METHOD OF DEGASSING A LIQUID FLOWING IN A FILM ALONG THE INNER PERIPHERAL SURFACE OF A ROTATING CENTRIFUGE ROTOR, WHICH COMPRISES DIVIDING THE LIQUID, BEFORE IT LEAVES THE ROTOR, INTO A FRACTION HAVING A LOW GAS-BUBBLE CONTENT AND A FRACTION HAVING A HIGH GAS-BUBBLE CONTENT, SEPARATELY REMOVING THE FRACTION HAVING A HIGH GAS-BUBBLE CONTENT, AND SEPARATELY REMOVING THE LIQUID FRACTION HAVING THE LOW GAS-BUBBLE CONTENT FROM THE ROTOR IN A MANNER TO MINIMIZE THE ADDITION OF FURTHER GAS-BUBBLE THERETO. 